Prism Coupling Technique Research Articles

Rare Earth Doped SnO<SUB>2</SUB> Nanoscaled Powders and Coatings: Enhanced Photoluminescence in Water and Waveguiding Properties

Luminescent Eu3+ and Er3+ doped SnO2 powders have been prepared by Sn4+ hydrolysis followed by a controlled growth reaction using a particle's surface modifier in order to avoid particles aggregation. The powders so obtained doped with up to 2 mol% rare earth ions are fully redispersable in water at pH > 8 and present the cassiterite structure. Particles size range from 3 to 10 nm as determined by Photon Correlation Spectroscopy. Rare earth ions were found to be essentially incorporated into the cassiterite structure, substituting for Sn4+, for doping concentration smaller than 0.05 mol%. For higher concentration they are also located at the particles surface. The presence of Eu3+ ions at the surface of the particles hinder their growth and has therefore allowed the preparation of new materials consisting of water redispersable powders coated with Eu(3+)-beta diketonate complexes. Enhanced UV excited photoluminescence was observed in water. SnO2 single layers with thickness up to 200 nm and multilayer coatings were spin coated on borosilicate glass substrates from the colloidal suspensions. Waveguiding properties were evaluated by the prism coupling technique. For a 0.3 microm planar waveguide single propagating mode was observed with attenuation coefficient of 3.5 dB/cm at 632.8 nm.

The effect of Fe 3+ doping in Potassium Hydrogen Phthalate single crystals on structural and optical properties

This work investigates the influence of iron doping on Potassium Hydrogen Phthalate (KHP) single crystals by the slow evaporation solution growth technique. Factors such as evaporation rate, solution pH, solute concentration, super saturation limit, etc. are very important in order to have optically transparent single crystals. As part of the work, the effects of metallic salt FeCl 3 in different concentrations were analyzed with pure KHP. Powder X-ray diffraction suggests that the grown crystals are crystallized in the orthorhombic structure. The functional groups and the effect of moisture on the doped crystals can be analyzed with the help of a FTIR spectrum. The pure and doped KHP single crystal shows good transparency in the entire visible region, which is suitable for optical device applications. The refractive indices along b axis of pure and doped KHP single crystals were analyzed by the prism coupling technique. The emission of green light with the use of a Nd:YAG laser ( λ=1064 nm) confirmed the second harmonic generation properties of the grown crystals.

Multiple beams surface plasmon interference generation: A theoretical analysis

In this paper, multiple beams surface plasmon (SP) interference generation based on prism coupling technique is theoretically analyzed and presented. The proposed multiple beams SP interference configuration is investigated for nanolithography application for two-dimensional feature fabrication. The configuration is then numerically and experimentally analyzed by employing aluminum metal at 364-nm illumination wavelengths to realize high resolution and high aspect ratio two-dimensional periodic nanoscale dot array patterns on the recording medium.

Judd-Ofelt Spectroscopic Study of Er:In:LiNbO3 Crystals For Integrated Optics

Er:In:LiNbO3 crystals were grown by Czochralski method from congruent melts containing 0.5/0.5, 0.5/1.0, and 0.5/1.5 mol%/mol% Er2O3/In2O3. The Er and In concentrations in the crystals were determined by neutron activation analysis. The refractive indices at the 473, 633, and 1536 nm wavelengths were measured by prism coupling technique. The unpolarized Er3+ and OH− absorption spectra of the crystals were measured at room temperature. The Er3+ absorption cross-section spectra were determined, and the Er3+ spectroscopic properties were analyzed by Judd–Ofelt (J–O) theory. The In segregation coefficient is 1.20 ± 0.06, 0.95 ± 0.05, and 0.89 ± 0.05, respectively, and the Er concentrations in all of the three crystals studied have a nearly same value of 1 mol%. The ordinary index decreases while the extraordinary index increases with the increased In doping level. The 0.5 and 1.0 mol% In2O3-doped two crystals are below while the 1.5 mol% In2O3-doped crystal is above the photorefractive threshold concentration. The Er3+ absorption cross sections of some transitions change definitely due to In codoping, but reveal a weak dependence on the In2O3 doping level. The J–O-predicted spectroscopic parameters show similar In codoping effects. The In codoping hardly affects the Er3+ 1.5 μm radiative lifetime.

X-ray photoelectron spectroscopy, high-resolution X-ray diffraction and refractive index analyses of Ti-doped lithium niobate (Ti:LiNbO3) nonlinear optical single crystal

Congruent LiNbO3 single crystals with Ti ion dopants (2 and 5 mol%) were successfully grown by Czochralski technique in the automatic diameter control facility. As-grown crystal boules were oriented into (0 0 1) direction cut and optically polished for all measurements. Influence of Ti-ion incorporation into LiNbO3 was studied by core level XPS analysis. Powder X-ray diffraction studies were carried out on doped lithium niobate for phase identification. High-resolution X-ray diffraction technique was used to study the crystalline quality through full-width at half-maximum values. The refractive index values are more for doped samples than for pure sample as determined by prism coupling technique with different laser sources.

Electro-optic characterization of epitaxial Ba 0.7Sr 0.3TiO 3 thin films using prism coupling technique

In this work, we present our study on evaluating electro-optic properties of Ba 0.7Sr 0.3TiO 3 thin films by prism coupling technique. Ferroelectric Ba 0.7Sr 0.3TiO 3 thin films were epitaxially deposited on LaNiO 3 electroded MgO (001) single-crystal substrates using pulsed laser deposition. Refractive indices and thickness of the Ba 0.7Sr 0.3TiO 3 thin film were determined with a rutile prism (Metricon 200-P-2) under zero electric field at a wavelength of 632.8 nm. The angular shift of guided mode was observed subsequently with a conductive prism (Metricon 200-P-4aC) when electric field was applied to the thin film sample. The ordinary refractive index n o changes 2.2% under a dc voltage of 4 V ( E ∼ 11 V/μm). The linear electro-optic coefficient tensor r 13 is thus calculated to be about 780 pm/V, showing the excellent potential of Ba 0.7Sr 0.3TiO 3 thin films for use in active optical devices.

Optical waveguide and nonlinear properties of Bi3NdTi3O12 thin films

Neodymium-substituted bismuth titanate (Bi3NdTi3O12, BNT) thin films were prepared on quartz substrates by a metal-organic solution deposition process. The crystalline structure was evaluated by X-ray diffraction. Waveguide property was investigated by using prism coupling technique and optical transmittance measurement. The optical nonlinearities of the film were measured by the top-hat Z-scan techniques and a large positive nonlinear refractive index, nonlinear refractive coefficient and two-photon absorption coefficient were determined to be 3.84 × 10−7 esu, 0.7523 cm2/GW and 4.81 × 104 cm/GW, respectively. These results reveal that the BNT film may be a kind of new multifunctional materials.

The Structural, Thermal, and Optical Analyses of Multicomponent Germanium Oxide Glasses for Engineering Mid‐Infrared Fiber Chemical Sensing

We demonstrate the suitability of multicomponent germanium oxide (GeO2)‐based glasses for engineering on‐line chemical sensors operating in the 2–5 μm spectral region. Bulk glass samples based on the oxide and oxy‐fluoride multicomponent compositions GeO2–PbO–Na2O, GeO2–PbO–Na2O–Ga2O3, and GeO2–PbO–Na2O–Ga2O3–PbF2, respectively were analyzed for comparing thermal, structural, and optical properties. These glasses were melted using in an oxygen‐rich atmosphere above 1200°C, and annealed after casting before undertaking detailed thermal analysis. Glass compositions with especially high fluoride and lead concentrations are reported to have the glass transition temperature above 350°C, which makes them suitable for operation in the 150°–200°C temperature range for chemical sensing and process metrology. The effects of composition on the thermal, structural, and optical properties of these glasses are studied using differential thermal analysis, Raman and infrared reflection spectroscopy, and prism coupling techniques. The compositional and wavelength dependence of refractive indices are also analyzed from which the value of the zero dispersion wavelength was determined.

NANOSCALE ARRAYS IN LITHIUM NIOBATE FABRICATED BY INTERFERENCE LITHOGRAPHY AND DRY ETCHING

Channel waveguides have been fabricated in x-cut lithium niobate (LiNbO3) by proton exchange (PE) method and optically measured. The thickness and the optical constants of the thin PE layer were characterized using a prism coupling technique. The PE area was plasma etched and a 2.775-μm total etching depth was achieved. The measured average etching rate is 92.5 nm/min. One- and two-dimensional dense arrays of LiNbO3 nanostructures have also been fabricated by using interference lithography (IL) and inductively coupled plasma reactive ion etching (ICP-RIE) techniques.

Third-order nonlinear and planar waveguide properties of TiO2/organically modified silane hybrid films doped with different disperse red 1 content

TiO2/organically modified silane organic–inorganic hybrid films doped with different disperse red 1 contents are prepared by combining a low-temperature sol–gel method and a spin-coating process. Effects of the disperse red 1 content on the third-order nonlinear and the planar waveguide properties of the hybrid films are also studied by a z-scan technique and a prism coupling technique. Results indicate that the nonlinear refractive index of the hybrid films is negative, whose magnitude is of the order of 10−8 esu for the measured samples. It is suggested that both the thermal effect and the photoisomerization process contribute to the third-order nonlinear optical properties of the hybrid films jointly. It is also found that the refractive index and the thickness of the hybrid films decrease with an increase of the temperature as the independent variable. In addition to, optical absorption properties of the hybrid films are characterized by UV–Visible spectroscopy. These results indicate that the as-prepared hybrid films are promising candidates for photonic applications.

Fabrication and investigation of 1D and 2D structures in LiNbO 3 thin films by pulsed laser ablation

Lithium niobate thin films were deposited on sapphire substrate by radio-frequency magnetron sputtering technique. One and two dimensional structures have been made using a KrF excimer laser at 248 nm and 6 ns pulse width, under various conditions of ablation, in order to assess the applicability of laser direct-writing of photonic waveguides. The optical and waveguiding properties of LiNbO 3 thin films were studied by prism-coupling technique, while micro-Raman spectroscopy was used for structural and composition characterization, as well as laser processing mechanism investigation. The surface morphology of the processed structures was obtained by a Nomarski optical microscope, an atomic force microscope and a White Light Interferometer Microscope.

Influence of dopant concentration on the structural and optical characteristics in Ti doped (2 and 5 mol%) LiNbO 3 nonlinear optical single crystal

Congruent lithium niobate single crystal with titanium ion dopant (2 and 5 mol%) has been successfully grown in an air by Czochralski technique with Automatic Diameter Control facility. The results of analysis of the influence of the Ti dopant concentration on X-ray diffraction, refractive index, optical absorption edge and FTIR in lithium niobate single crystals were presented. High Resolution X-ray Diffraction technique was used to study the crystalline quality through full width half maximum values with the presence of dopant incorporation. The increase of refractive index values observed for doped samples than pure sample by prism coupling technique with different laser sources. The position of the fundamental absorption edge in the near UV region was analyzed by UV–Vis spectra. FTIR spectra revealed that 5 mol% Ti doped lithium niobate crystals clearly suppresses the OH − defect sites than 2 mol% which indicates the limited influence of the humidity. The reason for OH − defect site suppression is discussed. Also the obtained results from all measurements are compared with pure congruent lithium niobate crystal.

Refractive index of high-carrier-doped InGaAs/AlAsSb coupled double quantum wells

The carrier density dependence of the refractive index of Si-doped InGaAs/AlAsSb coupled double quantum wells (CDQWs) was studied. The refractive index of the CDQWs changed due to two effects that arose from: (1) a change in the optical absorption and (2) the carrier plasma effect. The refractive index changes due to these two effects were separately evaluated by experimental methods and found to agree well with reference values obtained by a prism coupling technique. By considering the carrier density dependence of the refractive index of the CDQWs and the fundamental requirements for practical devices, we found that the carrier density of the CDQWs should be low with sufficient optical absorption strength due to intersubband transitions

Simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films using prism coupler technique

We present a simple method for simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films by measuring the film refractive indices as a function of temperature (dn/dT). Usually, such dn/dT value is considered as the thermo-optic coefficient. However, in the thin film systems, the measured dn/dT values result from both the thermo-optic and stress-optic effects. To demonstrate the stress-induced effects, the dn/dT values have been investigated for two different polymers: benzocyclobutene (high film stress) and epoxy 3505 (negligible film stress), using a prism coupler technique. The finite element method has been used so as to predict the stresses in the polymer film and, by combining them with the experimental dn/dT values, the individual thermo-optic and stress-optic coefficients have been determined. We found that the obtained thermo-optic coefficient is significantly different than the measured dn/dT values. The method is generic in nature and can thus be applied to a wide range of polymer waveguide materials.

Optical characterization of ferroelectric glycinium phosphite single crystals

Single crystals of glycinium phosphite (GPI) were grown by isothermal evaporation and conventional temperature-lowering techniques. Single crystal and powder X-ray diffraction analysis confirm the monoclinic structure of the as grown crystals. The structural perfection of the as grown crystal was determined through HRXRD analysis. FTIR and Raman analysis revealed the functional groups present in the grown crystals. The optical absorption of the grown crystal was analyzed and the refractive index values for different wavelengths were measured by prism coupling technique. Thermal stability, melting temperature and phase transition temperature of the as grown crystals were identified from TGA/DSC analysis. The dielectric impedance analysis indicates the continuous phase transition nature of the grown crystals. The mechanical strength and hardening co-efficient were determined from Vicker's microhardness measurements for different loads with constant dwell time. The growth mechanism and the defects were analyzed through chemical etching analysis from various crystallographic planes and etching periods.

Epitaxial Sr1.8Ca0.2NaNb5O15 thin film waveguides grown by pulsed laser deposition: Optical properties and microstructure

Epitaxial Sr1.8Ca0.2NaNb5O15 (SCNN) thin films slab waveguide structures that support several low-loss transverse electric (TE) and transverse magnetic (TM) modes were grown on MgO(100) substrates by pulsed laser deposition. To optimize the waveguiding properties, the relationship between film microstructure and deposition temperature was investigated by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. The prism coupler technique provides for the refractive indices and structural anisotropy of the core SCNN films deposited at various temperatures. Characterization based on this technique is proposed as a mean to relate the surface morphology to optical features such as the full width at half maximum of the excited guide mode.

Investigation on optical properties of Bi2.85La0.15TiNbO9 thin films by prism coupling technique

Layered-perovskite ferroelectric Bi2.85La0.15TiNbO9 (LBTN) optical waveguiding thin films were grown on fused silica substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) revealed that the film is highly (00l) textured. We observed sharp and distinct transverse electric (TE) and transverse magnetic (TM) multimodes and measured the refractive indices of LBTN thin films at 632.8 nm. The ordinary and extraordinary refractive indices were calculated to be nTE=2.358 and nTM=2.464, respectively. The film homogeneity and the film-substrate interface were analyzed using an improved version of the inverse Wentzel–Kramer–Brillouin (iWKB) method. The refractive index of the film remains constant at n0 within the waveguiding layer. The average transmittance of the film is 70% in the wavelength range of 400–1400 nm and the optical waveguiding properties were evaluated by the optical prism coupling method. Our results showed that the LBTN films are very good electro-optical active material.

Optical cross couplers based on wet-etch processing of benzocyclobutene polymer

In this paper, a characterization process of benzocyclobutene (BCB 4024-40) polymer and its realization into optical devices are described. By using the prism coupling technique, the polymer film thickness for various coating speed and the refractive index have been measured. Based on these results, the optical waveguides and couplers have been fabricated using the wet-chemical etch processing technique to take advantage of the photosensitive nature of the polymer. By adopting the multimode interference technique (MMI), the fabricated 2 × 2 optical cross couplers have been testified to demonstrate a maximum crosstalk of −17.81 dB and maximum loss of 3.37 dB.

Thermo-optic properties of epitaxial Sr_06Ba_04Nb_2O_6 waveguides and their application as optical modulator

A prism-coupler technique was introduced to determine the refractive indices and thermo-optic coefficients of epitaxial Sr(0.6)Ba(0.4)Nb(2)O(6) (SBN) waveguides, in a temperature range covering the ferroelectric-paraelectric phase transition. A strong enhancement in the TO coefficient is observed near T(c). This strong enhancement is related to the critical change of the polarization. The values of dn(e)/dT are significantly larger than dn(o)/dT due to the larger quadratic electro-optic coefficient in TM polarization. In TM mode, the refractive index of SBN is increased by 1.3% as the temperature is increased to 160 degrees C. Our results suggest that SBN waveguide is a potential candidate for thermo-optic modulators and switches.

Preparation and optical properties of sol–gel derived organic–inorganic hybrid waveguide films doped with disperse red 1 azoaromatic chromophores

We report here on TiO 2/organically modified silane (ormosil) organic–inorganic hybrid waveguide films doped with disperse red 1 (DR1) azoaromatic chromophores and derived by a low-temperature sol–gel process for photonic applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrabutyl titanate are used as matrix precursor for the hybrid films. Third-order nonlinear and photo-responsive properties of the hybrid films are studied by using a z-scan technique and a UV–vis absorption spectroscopy. Results indicate that the hybrid films have a large third-order nonlinear susceptibility and an obvious trans-to-cis photoisomerization under UV light irradiation. The planar waveguide and structural properties of the hybrid films are also characterized by a prism coupling technique, thermal gravimetric analysis, and Fourier-transform infrared spectroscopy. These results indicate that the as-prepared hybrid films are promising candidates for integrated optics and photonic applications, which allow directly integrating on the same chip waveguide devices with the functionalized devices.